Boron chloride production from an alloy of boron with tantalum



March lS, 1 c. A. HUTCHISON, JRL. E'IIAL 2,589,391

BORON CHLORIDE PRODUCTION FROM AN ALLOY OF BORON WITH TANTALUM Filed Aug. 28, 1945 I N VEN TOR.

CLYDE A. HUTOEISON JR JAMES 5. SM IT WdM.

Patented Mar. 18, 1952 BORON CHLORIDE PRODUCTION FROM AN ALLOY F BORON WITH TANTALUM Clyde A. Hutchison, Jr., and James S. Smith, New York, N. Y., assignors to, the United States of America as represented by the United States Atomic Energy Commission Application August 28, 1945, Serial No. 613,159

3 Claims.

This invention relates to a method and apparatus for recovering boron from its alloys, particularly from alloys which have been formed in a process for producing elemental boron; and for recovering the boron in a form which can be re-used in said process. This invention relates also to a method for determining the percentage of boron which may be recovered in the manner here described and to a method for determining the percentage of boron in an alloy.

One process of preparing elemental boron involves the vapor phase reduction of a boron compound in the vicinity of a heated metal rod, free boron being deposited upon the surface of the rod. More particularly, this process may be carried out by passing a mixture of boron chloride and hydrogen over a tantalum rod heated by means of an electric current, the reactants being contained in a suitable reaction chamber. Boron is deposited at the heated surface of the rod in accordance with the equation:

Tantalum, tungsten and molybdenum each has proved to be a useful material for the rod in View of the stability of these metals to the gaseous mixture employed. It has been found, however, that this stability is only relative and that even these stable metals react with boron to form alloys therewith.

When the outermost coating comprising elemental boron is removed from a tantalum rod which has been used in the above process,'the rod has been found to consist of an outer brittle portion comprising a boron-tantalum alloy containing about of boron by weight and an inner ductile portion which is substantially pure tantalum. By the term alloy is meant a solution of metals, or a definite compound of metals, or a solution of a compound of metals in a metal, or a mixture of metals.

It has further been found that the xtent of alloy formation depends on the length of time in which the tantalum rod is treated with the gaseous mixture of boron chloride and hydrogen.

If the reaction is allowed to proceed long enough the entire rod'reacts and consists entirely of the alloy. Processes have been developed for producing highly valuable isotopic species of boron chloride containing particular isotopes of boron in high concentration. When these isotopic species of boron chloride are used in the described process for preparing elemental boron it is desirable to recover any boron which has become alloyed with the metal of the rod. Since the extent of alloy formation varies directly with the time of treatment, there is the possibility of a considerable loss of valuable boron which it is desirable to recover, preferably in a form which can be re-used in the process for preparing elemental boron.

It is therefore an object of the present invention to recover the boron from an alloy of the element with a metal, particularly when the alloy has been formed in the described process for preparing elemental boron and may comprise, for example, an alloy of boron with tantalum.

Another object of the invention is to recover the boron from its alloys in a form in which it may be readily re-used in said process.

Another object of the invention is to recover boron which has undergone isotope concentration, from its alloys.

Further objects of the invention are to devise apparatus for accomplishing the recovery of boron from its alloys and methods for determining the percentage of boron which may be recovered and for determining the percentage of boron in the alloy.

According to the invention, boron may be separated from its alloys with one or more metals by treating the alloy with a halogen to produce the corresponding boron halide. The .boron halide may be separated from the reaction mass by various methods. According to a preferred method, the temperature of the reaction mass is regulated to produce a polyphase system and a phase containing the boron halide is separated. The latter phase may still contain some of the reactants and reaction products; in this event the temperature is again adjusted to produce a polyphase system and a phase containing boron halide of greater purity is separated. By a series of temperature adjustments to produce polyphase systems and the separation of phases containing the boron halide in successively increased purity, pure boron halide may be obtained. The separation of the phases of a polyphase system may involve separating a gas from a liquid or a solid; or a liquid from a solid; or two immiscible liquids from each other. In many cases the boron halide may be produced in a phase distinct from the phase comprising the alloy. It is then desirable to use a continuous flow system in which during the progress of the reaction, the phase containing the boron halide is continuously separated from unreacted alloy, and fresh halogen is continuously added to the alloy whereby complete conversion may be accomplished in a relatively short time. The phase containing the boron halide may then be purified, if necessary, by temperature adjustments, as described.

In this manner boron may be recovered from its alloys with one or more other metals and in particular from its alloys with tantalum, tungsten or molybdenum.

According to a preferred embodiment, boron is recovered from its alloy with tantalum by continuously passing chlorine gas over the alloy at a temperature preferably between '575" C. to 900 C., continuously separating gaseous reaction products comprising tantalum chloride, boron chloride and chlorine from unreacted alloy, continuously condensing tantalum chloride from these gaseous products and continuously separating a gaseous mixture of boron chloride and chlorine from the condensed tantalum chloride. The gaseous mixture of boron chloride and chlorine is liquefied and then fractionally distilled to vaporize the chlorine.

Accordng to another feature of the invention the percentage of boron which may be recovered in the form of boron halide may be determined by determining the weight of boron in the alloy sample to be treated, introducing the boron halide produced into an aqueous medium and determining the weight of boron in the resulting aqueous phase. The boron halide introduced into the aqueous medium is purified sufficiently to permit an accurate determination.

According to a further feature of the invention the percentage of boron in an alloy may be determined by completely converting the boron in a Weighed alloy sample to a boron halide, introducing the boron halide into an aqueous medium and determining the weight of boron in the resulting aqueous phase. In general, complete conversion may be effected when the boron halide is produced in a phase distinct from the phase comprising the alloy so that a continuous flow system may be used in which the boron halide is continuously separated from unreacted alloy and fresh halogen is continuously added.

The invention will be described in relation to the conversion of the boron in a boron-tantalum alloy to boron chloride,-and with reference to the figure which illustrates suitable apparatus for this purpose.

Referring to the figure, the apparatus may comprise asteel tank I containing chlorine gas connected to a gas drying unit consisting of the gas bubblers 2 and 3 in series, a reaction tube 4 connected toan outlet tube of the gas bubbler 3 and a steel unit generally designated by 5 connected as a receiver to the tube 4. The gas supply tank is provided with a tank valve 6 and a needle valve 1 for regulating the rate of gas flow. The gas bubblers 2 and 3 may comprise glass bottles partially filled with a drying liquid such as sulfuric acid and may have an internal helix as shown to cause the gas to traverse a longer path through the drying liquid. Inlet tubes 8 and 9 carry the gas into the liquid of each bubbler and outlet tubes l0 and II carry the dried gas out of each bubbler and toward the reaction tube. The reaction tube 4 is advantageously made of a high melting glass or of quartz and is provided with a ground stopper [2 of similar material which forms a removable, gas-tight closure. The

outlet tube II from the gas bubbler 3 includes a gas meter [3 and may be bent to form a right angle joint with a wall of the tube 4. The latter tube accommodates a receptacle for the alloy such as a fused silica boat M which is placed relatively closer to the gas input end of the tube adjacent the gas bubblers than to the opposite end. An electrical heating unit [5 is arranged to heat the reaction tube in the vicinity of the boat M and may comprise a block of insulating material having an opening adapted to receive the tube and provided with electrical heating elements at the surfaces of the opening. The block of insulating material may be formed of two halves joined by a hinge and thus may be opened to permit observation of the boat as the reaction progresses. Temperatures may be determined during the progress of the reaction by inserting an iron-constantan thermocouple IS in the space H between the reaction tube and the heating unit and taking readings on a potentiometer l8 associated with the thermocouple. A valve I9 in the outlet tube 29 from the reaction tube 4 serves to isolate the reaction tube from the receiver assembly and a union 2! permits the two parts of the system to be detached. The receiver assembly 5 comprises a receiving can 22 placed within an insulated can holder 23. When the apparatus is in use a packing of a refrigerant such as solid carbon dioxide is placed between the can and the holder. A tube 24 leading from the union 2| is welded to the can and dips into it. The receiving can may be opened to the atmosphere through the drying tube 25 which is open to the air at the upper end'and is provided with a bulb portion 28 packed with a drying agent such as calcium chloride for drying the air which is admitted to the can 22 via the drying tube. Valves 21 and 23 serve to isolate the receiving assembly from the atmosphere when, for example, it is disconnected from the rest of the system at the union 2 I.

Ordinary tank chlorine may be used when the gas bubblers filled with a liquid such as sulfuric acid are employed to dry the gas and thus purify it. The efficiency of the bubblers as gas driers depends on the time of contact of the gas with the sulfuric acid; two units may be employed as shown or one large unit of equivalent drying capacity. Boron chloride is hydrolyzed by water and therefore to obtain optimum yields it is desirable to exclude moisture from the reaction chamber. These considerations apply equally when other halogen gases are used to produce the corresponding boron halides.

A sample of tantalum rod which has been used for the production of boron by the vapor phase reduction of a volatile boron compound and from which elementary boron has been removed, is crushed until the brittle portion comprising the boron-tantalum alloy achieves a fineness of subdivision permitting it to pass'through a 50-mesh screen. A charge of the-alloy is placed in the boat I4 which may be inserted in the tube 4 when the stopper [2 is removed. The valves 6 and I of the chlorine supply tank are adjusted and chlorine gas is passed through the system until all air is removed. After this flushing the receiving can 22 is placed in the holder 23 which contains solid carbon dioxide. The flow rate of chlorine to the reaction tube is adjusted to permit a desirable reaction speed and to avoid excessive Waste of the gas, indications of the flow rate being obtained by means of the flow meter [3. The temperature of the reaction chamber in the vicinity of the boat i4 is raised by means of the heating unit IE to 900 C. and held at that temperature until it appears that the alloy has ceased reacting. The receiving assembly is then disconnected from the rest of the apparatus at the union 2|. The receiving can 22 contains a liquid product consisting of boron chloride mixed with chlorine. Solid yellow tantalum pentachloride forms a deposit in the cold part of the reaction tube. The liquid mixture is transferred to a fractional distillation apparatus (not shown) and distilled. Since chlorine has a much lower boiling point than boron chloride and forms no constant. boiling mixtures therewith, it is readily removed as volatile matter to leave liquid boron chloride in pure form. This product may then be converted to the gaseous phase and used in the described process for producing elemental boron.

Experimental studies of this reaction indicated that the boron may be completely recovered at temperatures in the range of 575 C. to 900 C. Boron chloride is evolved at temperatures below 575 C. but at a slower rate.

In order to determine the percentage of boron recovered, the above procedure may be used with modifications. A sample of the alloy is analyzed for its boron content by fusing the sample with a mixture of sodium hydroxide and sodium carbonate, dissolving the melt in water, acidifying the aqueous solution and filtering off tantalum oxide. The aqueous filtrate remaining contains boric acid which is titrated to determine the boron content of the alloy sample. Another sample of the alloy is carefully weighed and its boron content is determined on the basis of the analyzed sample. The carefully weighed sample is placed in the boat It and treated with chlorine gas in the described manner. The gaseous mixture of boron chloride and chlorine is trapped in a water bath instead of being condensed. For this purpose the receiver assembly 5 is replaced by an Erlenmeyer flask or several of them (not shown) containing water,

The aqueous solution is analyzed to determine the percentage of boron recovered, by titrating a sample of the solution with standard alkali to a Recovery of boron from boron-tantalum alloys Weight of Total B Recovery Run Starting Present 35E 3? of B Material g. mg. Percent This method of determining the percentage of boron recovered is of general application in the treatment of boron-metal alloys with a halogen to produce a boron halide. The boron halide need not necessarily be in the form of a gas when it is introduced into the aqueous medium but may be in a liquid or solid form.

The figures in the table indicate that, with the procedure described, the conversion of boron in the boron-tantalum alloys to boron chloride was complete. Hence the procedure may be adapted to determine the percentage of boron present in these alloys. To 'carry out the determination, a sample of the alloy is carefully weighed and treated to produce boron chloride in the described manner. The boron chloride is introduced into water and the resulting aqueous solution is analyzed to determine the boron content.

This method of determining the percentage of boron in an alloy is available when the boron halide is produced in a phase distinct from the phase comprising the alloy. By use of a continuous flow system in which the distinct phase comprising the boron halide is continuously separated from unreacted alloy and fresh halogen is continuously added, complete conversion may be accomplished in a relatively short time.

Further modifications in the, apparatus and methods may be made without departing from the scope of the invention. For example, the reaction tube may be made of a material other than high melting glass or quartz provided it is not affected under the conditions of the reaction. The Proportions of the reaction tube may be altered. The gas bubblers may be replaced by other types of drying units. The tantalum chloride may be condensed in a separate receptacle maintained at a suitable temperature, instead of in the reaction tube. If desired, the tantalum chloride need not be continuously condensed as it is formed but the gaseous reaction products comprising tantalum chloride, boron chloride and chlorine may be completely collected first and then subjected to suitable condensation and evaporation steps to obtain pure boron chloride. Instead of purifying the boron chloride by taking advantage of the difference between the boiling point (or the melting point) of boron chloride and of the substances with which it is in a homogeneous phase, purification may be effected in other ways such as by dissolving the boron chloride in, a selective solvent and separating the solution. It is preferred to continuously separate gaseous boron chloride from unreacted alloy as the reaction progresses. On the other hand the reaction may be allowed to proceed until it ceases before any product is separated. Other halogens such as bromine, iodine and fluorine may be used in'place of chlorine to recover the boron from boron alloys and the latter may comprise alloys of boron with tungsten, molybdenum or any other metal or metals with which boron may be alloyed.

Since many embodiments might be made of the present invention and since many changes might be made in the embodiment described, it is to be understood that the foregoing description is to be interpreted as illustrative only and not'in a limiting sense.

We claim:

1. A method for recovering the boron from an alloy of boron with tantalum which comprises treating the alloy with chlorine at a temperature between 575 C. and 900 C., condensing the resulting tantalum chloride and maintaining the resulting boron chlorine in a gaseous phase to produce a polyphase system, separating said gaseous phase containing boron chloride from said polyphase system and isolating boron chloride from said separated phase.

2. A method for recovering the boron from an alloy of boron with tantalum which comprises continuously passing chlorine gas over the alloy at a temperature between 575 C. and 900 C., continuously separating gaseous reaction products from unreacted alloy, continuously condensing tantalum chloride from said gaseous reaction products and continuously separating a gaseous mixture of boron chloride and chlorine from said condensed tantalum chloride.

3. A method for recovering the boron from an 7 alloy of boron with tantalum which comprises continuously passing chlorine gas over the alloy at a temperature between 585 C. and 900 C., continuously separating gaseous reaction products'from unreacted alloy, continuously condens- 5 ingtantalum chloridefrom said gaseous reaction products, continuously separating a gaseous mixture of -boron chloride and chlorine from said con densed tantalum chloride, liquefying said mixture and fraction'ally distilling said mixture to 10 obtain pure boron chloride.

CLYDE A; HUTCHISON, J R., JAMES S. SMITH.

REFERENCES CITED The 'foilowing references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Inorganic and Theoretical Chemistry by J. W. Mellor, vol. 5, pp. 26-32, 122 and 130., and vol. 9, pp. 915, 920, Longmans, Green & Co., -N. Y. 

1. A METHOD FOR RECOVERING THE BORON FROM AN ALLOY OF BORON WITH TANTALUM WHICH COMPRISES TREATING THE ALLOY WITH CHLORINE AT A TEMPERATURE BETWEEN 575* C. AND 900* C., CONDENSING THE RESULTING TANTALUM CHLORIDE AND MAINTAINING THE RESULTING BORON CHLORINE IN A GASEOUS PHASE TO PRODUCE A POLYPHASE SYSTEM, SEPARATING SAID GASEOUS PHASE CONTAINING BORON CHLORIDE FROM RIDE FROM SAID SEPARATED PHASE. 